Characterization of Staphylococcus aureus based on its virulence determinants and antibiotic resistance profile

Abstract

newline Research focus: Staphylococcus aureus infections are difficult to treat due to various virulence determinants and multiple antibiotic resistance determinants like MRSA. Treatments have become further complicated with the emergence of Vancomycin Intermediate S.aureus (VISA) and the rise in heteroresistant VISA (hVISA) population among methicillin susceptible and resistant isolates. Also there always remains a difficulty in detecting these isolates by routine CLSI guidelines. Therefore, improvements in screening and confirmatory tests to detect these isolates as well as delineating specificity of accessory gene regulator (agr), a global virulence determinant are required. newlineMaterials and Methods: A total of 468 non- duplicate S.aureus strains were included in the study. MRSA isolates and hVISA/VISA isolates were detected by screening and confirmatory methods (MRSA screen by cefoxitin disc, hVISA/VISA screen by brain heart infusion agar with 6µg vancomycin and hVISA/VISA confirmation by PAP-AUC method). Agr polymorphism in hVISA/VISA was analyzed by duplex PCR. Agr dysfunction if any, in these strains was studied by their colony spreading property and autolytic property using soft agar and Triton X-100 induced lysis, respectively. newlineResults: Out of 468 S.aureus strains, 24% strains were detected as MRSA and 7.0% were hVISA/VISA strains. Among MRSA detected 13% strains were confirmed as hVISA/VISA. All hVISA/VISA isolates showed reduction in autolytic activity and colony spreading property was appreciated in 39% of these isolates. Out of the 33 hVISA/VISA strains, a majority belonged to agr I, III and II and the least belonged to agr IV. newlineConclusion: It is concluded that hVISA/VISA strains have diverse virulence properties and are detected in both MRSA and MSSA strains. Therefore surveillance of these strains among S.aureus isolates having vancomycin MIC s and#8804;1.5 µg/ml in laboratory settings is needed.